Process of producing phosphoric acid



gen, which is very valuable for various syn- Patented Mar. 15,1 1932 UNITED STATES} EDCSUARDQ URBAI N or PARIS, matron; iissldilron; JYlMESNEi lissierivmnirrsg rd PAGNIE DES PRODUITS'GHIMIQUES E'r-cnARBoNs norms nn. URBAVIN, on 1131s,; FRANCE, A CORPORATION or FRANCE we I 1 I :rxoons's or rnonncme rfiosrnomc'ACID No Drawing. Application filedi lApril 2 1927, Serial-No. 185,662, and in France December}; 1926,

The present invention relates primarily to ajprocess which in 'its entirety isdirected to obtaining products of value from phosphate rock; but" certain phases ofthe process will have otherand broader'applications. V 7

As related'to phosphaterock; the first phase'of the invention consists in treating phosphorus rock together with other basic r, ingredients and carbonin such a way that a At the same time; substantially none of the carbon-mono xidejis oxidized, so that as' a result of the second phase'of the operation,

mixture of phosphorus vapor and carbon monoxide is obtained which may be some-' what diluted with other inert gases. .As an} incident to this phase of the process I may .,0bta-in"active carbon and calcium sulphate or a slag havingth v fl q setting'cement; V r

"In thesecond phase of theprocessth forev going mixture of gases and vapors is subjectedto the actionof steam under'such con;

ditions; that the phosphorus is oxidizedtoj form phosphoric acid which is separatedout, and hydrogenis added to the gas mixture.

I obtain commercially pure phosphoric acid Well adapted for many purposes such 'as the; manufacture of ammonium phosphate and a mixture of carbon-monoxide and hydrothetic processes such for example as the manufacture of methanol;

In the first'part of the'process the P0 radical containedinthe phosphate rock (tricalcium phosphate)- is caused to react with 7 carbon containing substances under condi tions which will prevent the extensive formation of CO This may bedone either indirectly or directly as is illustrated by the two following examples:

.(1) Phosphate rock is treated with sulphuric acid to produce calcium sulphate and crudepho'sphoric acid. The phosphoric acid is then heated to a high temperature in'the presence of carbon containing material without admission of substantial quantitiesof oxygen, until there is an evolution OfPhOS- phorus. This stage of the-process is prefcember '14, 1926, whereby there is obtained active carbon adapted for absorption' or de-" colorizing' work, and vapors of: phosphorus mixed'with carbon monoxide'; i

(2) F or the'direct method, the phosphate earlier l atent No. 1,610,399, dated-Derock may be heated'in the presence of carbonto which I prefer to add silica and alumina:

(bauxite) or amixture of alumina and cl'ay.

Sufficientcarbon must be present to produce:

the reaction P O5+5C=2P+5COL- If the production-is conducted in an electric furn'ace; the exact amount of; 'carbon for the reaction isall: that need be'addedg though a: small excess will do no harm as itcan-readily be burned out by'admitting'air to -the' fur 'nace after the evolution of phosphorus has ceased; On the other. h-and, if the reaction is conducted in anordmary vertical furnace,

additional carbon should be added 'suflicientiv eso so it can be burnedto heat the charge to a v temperature ofab'out l600 C. (which is an terial necessary will depend-upon its ash con tent an'd'the richness of the phosphate rock. In this case there will be some=variation in the amount ofcarbon' monoxide'fo'rmed, but care should be taken'tolimitthe amount of economicaltemperature to use though it may oxygen admitted and so to carry on thecom- I bustionas to prevent the extensive formation OfCO There will also be some'nitrogen mixed with the resulting vapors.- a

' If the phosphate rock were simply" heated- With the carbon the desired vapors and gases would be' 0btained;, but the residual? slag would l;)e '-valueless. When silica 'a'nd 'alu-i mina' are added these ingredients Will com binewiththe calcium liberated bythe evolh; I

tionof phosphorusand give=a slag having 'thefc omposition of quick-setting cement so; I thatja valuable residue is obtainedat very little t on "dose ditionsf affecting: the costs of raw materials 59; erably conducted in the manner described in hauxitefand the valuejof The'question of hich p mee mie a renew 'willhorjdinarily depend on the marketijconr phosphorus can be treated with steam to form phosphoric acid and hydrogen. Id owever, un-

less a very high temperature (above 800 C.)

is used,-the production of phosphoric acid by this method is impractical owing to the formation of hydrogen phosphides. This high temperature has many disadvantages and for the purposes of the present process is quite impractical, for the same temperature used to cause an evolution of hydrogen will cause the carbon-monoxide to be further oxidized and rendered valueless.

. I have discovered that the desired reaction between the phosphorus and steam can be carried on commercially below thetemperature at which the carbon-monoxide is further oxidized, if the reaction is caused to take place in the presence of absorptive carbon such for example as that obtained in example 1 above. A catalyst'in the gaseous or vapor stage also should be used.

The absorptive carbon apparently serves as a catalyst sothat the, desired reaction will take place at as low a temperature as 350 C.

but if a higher temperature is used the reaction is accelerated. For example, at 700 C.

the reaction will be quite rapidwhile less than 1%'- of-the carbommonoxide will be consumed. In any event, the top limit is that. at which the active carbon will ignite. The useof the absorptive carbon further pros vides a ready means of separatingout the phosphoric acid which will be held as metaphosphoric acid in the carbon from which itv may readily be washed out. ,1

As regards thecatalyst for the oxidation of the phosphorus. by steam it is known that metallic substances can be used, but I have discovered that non-1netallic substances have a strong catalytic action when used in conjunction with the absorptive carbon. For example, one can easily and advantageously use a very small amount (1 part to athousand parts of phosphorus vapor) of a halogen or a halogen compound such as hydrochloric acid.

.In practice, Ifind it advantageous to take the vapors as they come from one of the types of furnace or retort used in the first phase, add an excess of steam and the gaseous catalyst, and pass the mixture through an absorber containing the active carbon. This may be heated to say 350 C. to start the reaction but as the reaction is exothermic, it may be found necessary to cool the gas mixture to prevent the temperature in the absorber from rising too high. For continuous operation,two absorbers maybe used so that when one is satu rated by phosphoric acid the other may be connected to the gas supply while the first is being washed with water to remove the phosphoric acid which is retained'in the carbon. The acid thus obtained will be technically pure so that itmay be usedfor example in the manufacture of ammonium phosphate.

'1 have found that for each kilogram of: phosphorus that was present about 1800 litres of hydrogen will be released, and since the carbon-monoxide has not been consumed the resulting gas mixture will be well adapted for many synthetic processes.

If one desires to obtain the hydrogen and carbon-monoxide separately, the vapors from the furnace or retort can be passed through a bed of active carbon (which will absorb the phosphorus vapors, so that, the carbon-monoxide may be collected and used as desired. The steam and catalyst may then be passed into the impregnated carbon so that the phosphorus is converted into metaphosphoric acid and hydrogen liberated. Any excess steam together with the catalyst can be condensed,

leaving the hydrogen substantially pure.

This hydrogen may be caused to combine with atmospheric nitrogen by any appropriate process to produce ammonia, which in turn may be passed through the phosphoric acid washed from the carbon giving a yield of ammonium phosphate.

In other words, I may start with phosphate rock, ordinary carbon containing material such as peat, sawdust, charcoal etc, air and steam together with either sulphuric acid or alumina and silica and produce calcium sulphate and active carbon or quick-setting cement, methanol, ammonia, ammonium phos phate and pure phosphoric acid as well as other synthetic products, with no other wa ste products to be disposed of. e

"What I claim isi V The process of converting phosphorus into phosphoric acid, which comprisesthe step of causing the phosphorus to react with steam mixed with a halogen containing substance as a catalyst in the presence ofabsorptive carbon at a temperature above 300 and below the combustion point of the carbon, whereby hydrogen is evolved and metaphosphoric acid is obtained absorbed in'thecarbon.

EDOUARD URBAIN. 

